after(n) Tcl Built-In Commands after(n)______________________________________________________________________________NAMEafter - Execute a command after a time delay
SYNOPSISafter ms
after ms ?script script script ...?
after cancel id
after cancel script script script ...
after idle ?script script script ...?
after info ?id?
_________________________________________________________________DESCRIPTION
This command is used to delay execution of the program or to execute a
command in background sometime in the future. It has several forms,
depending on the first argument to the command:
after ms
Ms must be an integer giving a time in milliseconds. The com‐
mand sleeps for ms milliseconds and then returns. While the
command is sleeping the application does not respond to events.
after ms ?script script script ...?
In this form the command returns immediately, but it arranges
for a Tcl command to be executed ms milliseconds later as an
event handler. The command will be executed exactly once, at
the given time. The delayed command is formed by concatenating
all the script arguments in the same fashion as the concat com‐
mand. The command will be executed at global level (outside the
context of any Tcl procedure). If an error occurs while execut‐
ing the delayed command then the bgerror mechanism is used to
report the error. The after command returns an identifier that
can be used to cancel the delayed command using after cancel.
after cancel id
Cancels the execution of a delayed command that was previously
scheduled. Id indicates which command should be canceled; it
must have been the return value from a previous after command.
If the command given by id has already been executed then the
after cancel command has no effect.
after cancel script script ...
This command also cancels the execution of a delayed command.
The script arguments are concatenated together with space sepa‐
rators (just as in the concat command). If there is a pending
command that matches the string, it is cancelled and will never
be executed; if no such command is currently pending then the
after cancel command has no effect.
after idle script ?script script ...?
Concatenates the script arguments together with space separators
(just as in the concat command), and arranges for the resulting
script to be evaluated later as an idle callback. The script
will be run exactly once, the next time the event loop is
entered and there are no events to process. The command returns
an identifier that can be used to cancel the delayed command
using after cancel. If an error occurs while executing the
script then the bgerror mechanism is used to report the error.
after info ?id?
This command returns information about existing event handlers.
If no id argument is supplied, the command returns a list of the
identifiers for all existing event handlers created by the after
command for this interpreter. If id is supplied, it specifies
an existing handler; id must have been the return value from
some previous call to after and it must not have triggered yet
or been cancelled. In this case the command returns a list with
two elements. The first element of the list is the script asso‐
ciated with id, and the second element is either idle or timer
to indicate what kind of event handler it is.
The after ms and after idle forms of the command assume that the appli‐
cation is event driven: the delayed commands will not be executed
unless the application enters the event loop. In applications that are
not normally event-driven, such as tclsh, the event loop can be entered
with the vwait and update commands.
SEE ALSObgerror(n), concat(n), update(n), vwait(n)KEYWORDS
cancel, delay, idle callback, sleep, time
Tcl 7.5 after(n)